1. Field of the Invention
The present invention provides an improved process for making higher aryl esters from higher aromatic compounds such as naphthalene, anthracene, biphenyl, phenanthrene, terphenyls, and the like, which comprises reacting a solution of the higher aromatic compound, such as a solution of naphthalene in hexane, with molecular oxygen and a higher carboxylic acid in the liquid phase in the presence of a catalyst which is composed of palladium or a compound of palladium, a compound of antimony and optionally a compound of a metal selected from the group consisting of chromium, cobalt, nickel, manganese, iron and tin.
2. Description of the Prior Art
The manufacture of phenol by the direct oxidation of benzene with oxygen is known. There are, for instance, thermal processes which are performed at very high temperatures in which the phenol formed is susceptible to further oxidation so that considerable loss of yield occurs as is disclosed in U.S. Pat. No. 2,223,383. In the presence of catalysts, the oxidation can be carried out at somewhat lower temperatures as in U.S. Pat. No. 3,133,122 but the reactions have been plagued by low conversions and excessive production of unwanted by-products as is disclosed in U.S. Pat. No. 2,392,875.
It already has been proposed to make phenyl acetate and biphenyl from benzene and acetic acid in the liquid phase in the presence of palladium acetate and without added molecular oxygen by a stoichiometric reaction in CHEM. AND IND., Mar. 12, 1966, page 457.
U.S. Pat. No. 3,542,852 discloses the preparation of hydroxy aromatic compounds by reaction of an aromatic compound and oxygen in the presence of a catalyst composed of iron, a noble metal or a compound of either in the presence of a nitrate ion and a carboxylic acid. More recently the preparation of phenyl esters and phenols by the reaction of benzene, molecular oxygen and a lower aliphatic carboxylic acid in the presence of a catalysts composed of a Group VIII metal (U.S. Pat. No. 3,642,873) or a compound of such metal (U.S. Pat. No. 3,651,127) have been disclosed. Similarly, variations in this type of reaction have been disclosed in U.S. Pat. Nos. 3,646,111; 3,651,101; 3,772,383; 3,959,352 and 3,959,354. U.S. Pat. No. 3,959,354 concludes that liquid phase reactions of this type because of problems of catalyst elution, etc. are disadvantageous for an industrial process. U.S. Pat. No. 3,772,383 describes a liquid phase reaction using a very complex catalyst system which includes the use of nitric acid and a lower aliphatic carboxylic acid such as acetic, propionic, n-butyric, isobutyric, or caproic acid. Generally speaking these prior art processes deal for the most part with vapor phase oxidation reactions, or liquid phase reactions in which all the reactants (except oxygen in some instances) are initially included in the reaction mixture, they use lower aliphatic carboxylic acids such as acetic acid and propionic acid, and they often require an alkali or alkaline earth metal carboxylate as part of the catalyst. Moreover, in general the prior art catalytic processes have produced very low conversions, usually less than 10%, with poor selectivity to the desired phenyl ester, and phenol is often a primary product. The use of the lower saturated carboxylic acids, primarily acetic acid, in the prior art processes produce a highly corrosive system which can cause reaction equipment problems and excessive recycle costs as well as the poor conversions and selectivities mentioned above. None of the prior art processes disclose the continuous addition of the aromatic hydrocarbon and the continuous removal of water from the reaction mixture as it forms nor do they disclose or suggest the use of a solvent for higher aromatic compounds in the oxidation process.